Block rotation induced by the change from the collision to subduction: Implications for active deformations within the areas surrounding South Caspian Basin

Abstract

Northern of Iran is experiencing a complex deformation due to the northward convergence of Arabian plate since late Cenozoic. The majority of this complexity is due to the presence of a rigid, old, thickened oceanic crust of the South Caspian Basin (SCB). This rigid block, trapping between Eurasia and Central Iran, makes an inhomogeneous body in the context of deforming zone composed by Alborz, Talesh, Apsheron-Balkhan, Caucasus, and Kopeh Dagh located in south, west, northwest, north, and east of the SCB, respectively. Among them, the formation and evolution of the Alborz orocline are under debates. The presence of sinistral strike-slip faults with normal separation initially understood by NW motion of northern Alborz inferred by GPS measurements raised long debates. In the latest proposition, it is assumed that the SCB is rotating clockwise. This study, however, shows that the model of SCB's rotation and/or NW-ward motion of SCB is not kinematically consistent. Therefore, it aims at constraining the Alborz, northern central Iran, and NW Iran, as a sliver block, are rotating around the SCB. The block rotation is facilitated by geo-sutures inherited since Paleozoic. Therefore, this article specifically pays attention to the active extensional tectonic regime as a signal for the area that is under rotational movement. The block rotation induced by the change from the collision (in Kopeh Dagh) to subduction (SCB and Kura Basin beneath Alborz, Talesh, Apsheron-Balkhan, and Great Caucasus, respectively), and consequently the reactivation of ancient geo-sutures in northern Iran led to a rapid rotation of microcontinents. This assumption may account for the ongoing deformational pattern in Alborz and NW Iran. The disharmonic Arabian plate convergence and SCB's retreating induce forces by the block rotation and cause episodic tectonic activities that are responsible for current tectonic complexity in the north of Iran. If the climax of the collision was ~5 Ma, then the block rotation and related deformation are younger events with respect to the collision and subduction.